Can you try downloading the latest hotfix or redownloading the engine fresh?
In the attached video you’ll see that I imported a .srt file, not an FBX, via the content browser. In the top right, it shows that I’m on 4.12.2 CL-3005592, which at the time of testing this, was the latest available hotfixed release from the Epic Games Launcher.
I’m not sure why you’re not able to see the option, but there is no difference in this version than what is publicly available. At the moment, my suggestion would be to download a fresh copy and see if this resolves the issue for you since I cannot reproduce what you’ve reported.